Measuring device with a plunge-in electrode

ABSTRACT

The invention relates to a measuring device, especially for measuring the pH value in food, comprising an extended first electrode ( 2 ) for plunging into a good to be measured ( 40 ) and a sheath ( 4 ) which at least partially surrounds said first electrode ( 2 ). The first electrode ( 2 ) is pivotally mounted in order to prevent breakage as a result of transversal loads exerted perpendicularly to the axial direction of said first electrode ( 2 ).

[0001] The present invention relates to a measuring device having an extended first electrode for being inserted into a material to be measured and having a sheath which at least partially surrounds the first electrode.

[0002] Such measuring devices are used, for example, for measuring the pH of foodstuffs such as meat, for example. Typically, a chamber is formed between the first electrode and the sheath in which a second electrode formed from a gel, for example, is installed. Both electrodes are connected to an evaluation circuit to determine the pH of a liquid of the material to be measured which has infiltrated between the electrodes.

[0003] For the measurement, the measuring device having the first electrode is pushed with great force into the material to be measured, resulting in a considerable mechanical load on the first electrode. First electrodes for pH measurement are usually made of glass, or have glass as the sheath, and can bear a high load in the axial direction and thus in the insertion direction. Perpendicular to the axial direction, these first electrodes are capable of bearing only a light load due to the brittleness of glass, which can result in breakage when a load is applied in this direction, as when the measuring device is tilted during insertion or withdrawal.

[0004] To avoid this problem, measuring devices have been provided in which the glass electrode or the gel surrounding the glass electrode is enclosed by a glass sheath and then by a metal or plastic sleeve. Although the load-bearing capacity of the glass electrode perpendicular to the axial direction does increase somewhat, the slightest deformations of the sheath, which are transmitted directly to the glass electrode, result in breakage of the first electrode and/or the glass sleeve surrounding the gel.

[0005] The double sheath made of glass and plastic also results in a larger diameter in the region of the probe tip, which during measurement creates large holes in the material to be measured.

[0006] The object of the present invention is to provide a measuring device having a first electrode which is more robust with respect to loads applied perpendicularly to the axial direction.

[0007] This object is achieved by a device according to the features characterized in claim 1.

[0008] According to the present invention, the extended first electrode for the measuring device is pivotably mounted so that when subjected to a load that is perpendicular to the axis, the first electrode is able to resist this load to a certain degree, thereby avoiding breakage of the first electrode, which preferably is designed as a glass electrode.

[0009] Advantageous embodiments of the present invention are objects of the subclaims.

[0010] In order for the first electrode to be able to pivot under a transverse load, it is necessary for the sheath to also follow a pivoting motion of the first electrode, in a direction perpendicular to the electrode axis. For this purpose, the sheath preferably is made of a flexible, non-brittle material such as a flexible plastic. According to one embodiment of the present invention, the bending characteristics of the sheath are improved by increasing a diameter of the sheath in the region of the holding fixture, or in the region of an “imaginary hinge point,” for the glass electrode. The imaginary hinge point is a point on the first electrode about which the first electrode is able to pivot as the result of an articulated support in the holding fixture, this point not changing its position when the first electrode pivots. In the first electrode according to the present invention, glass sheathing around the gel forming the second electrode is not required for stabilization.

[0011] The pivotable mounting for the first electrode is preferably created by a holding fixture which accommodates the first electrode at one end. To this end, the holding fixture preferably has a recess which accommodates the first electrode, a base region of the recess forming a support for one axial end of the first electrode. According to one embodiment of the present invention, lateral support for the first electrode is provided by arranging a ring-shaped element surrounding the first electrode between the first electrode and a side face of the recess. The ring-shaped element, which preferably is made of a flexible material such as an elastomer, in particular silicone, supports the glass electrode, at its end which is introduced into the recess, against the side faces of the recess in order to hold the first electrode essentially parallel to the side faces in a resting position when a transverse load is not present. Under a transverse load, the flexible ring-shaped element enables the first electrode to laterally pivot in order to avoid breakage of the first electrode.

[0012] According to one embodiment of the present invention, the ring-shaped element has an essentially circular cross-section similar to that of an O-ring, which surrounds the first electrode in the region of the opening in the recess and supports the first electrode against the side face. Below the ring and between the first electrode and the side face of the recess an air gap is formed which allows the end of the glass electrode to move sideways.

[0013] According to a further embodiment of the present invention, the ring-shaped element essentially has the design of a sleeve which partially or totally encloses the first electrode at the end section which is introduced into the recess. An elastic deformation of the sleeve allows the first electrode to pivot under a stress which is perpendicular to the axis.

[0014] According to a further embodiment of the present invention, a recess is provided with an essentially truncated cone-shaped design, a lower end of the recess having the smallest diameter and forming a support for an axial end of the first electrode. In this embodiment, lateral support of the first electrode is not provided in the recess. Due to the conical shape of the receptacle, the first electrode becomes “centered” in the initial position after the transverse load is removed. The lateral stability is essentially provided by the sheath, which surrounds the first electrode in at least one location. Lateral pivoting motions of the first electrode at the end which is introduced in the recess are made possible by the upwardly increasing diameter of the recess.

[0015] According to a further embodiment of the present invention, the first electrode is mounted using a ball-and-socket joint, the first electrode preferably being glued in place in a receptacle in one of the two joint halves.

[0016] In addition, according to the present invention the first electrode is secured in a receptacle in a flexible shank, preferably by gluing.

[0017] The present invention is explained in more detail hereinafter in exemplary embodiments, with reference to the figures.

[0018]FIG. 1 shows a detail of a measuring device according to the present invention, in a cross-sectional side view.

[0019]FIG. 2 shows a detailed illustration of a holding fixture for accommodating the first electrode according to a first embodiment, with the first electrode in the unswiveled (FIG. 2a) and swiveled (FIG. 2b) position.

[0020]FIG. 3 shows a detailed illustration of a holding fixture for accommodating the first electrode according to a second embodiment, with the first electrode in the unswiveled (FIG. 3a) and swiveled (FIG. 3b) position.

[0021]FIG. 4 shows a detailed illustration of a holding fixture for accommodating the first electrode according to a third embodiment, with the first electrode in the unswiveled (FIG. 4a) and swiveled (FIG. 4b) position.

[0022]FIG. 5 shows a detailed illustration of a holding fixture for accommodating the first electrode according to a fourth embodiment, with the first electrode in the unswiveled (FIG. 4a [sic; 5 a]) and swiveled (FIG. 4b [sic; 5 b]) position.

[0023]FIG. 6 shows a detailed illustration of a holding fixture for accommodating the first electrode according to a further embodiment, with the first electrode in the unswiveled (FIG. 6a) and swiveled (FIG. 6b) position.

[0024]FIG. 7 shows a detailed illustration of a holding fixture for accommodating the first electrode according to a further embodiment of the present invention; and

[0025]FIG. 8 shows a detail of a measuring device according to the present invention during measurement under a load exerted by lateral forces.

[0026] Unless indicated otherwise, identical reference numbers in the figures denote identical parts having the same meaning.

[0027]FIG. 1 shows a detail of a measuring device according to the present invention in a cross-sectional side view. The measuring device has an extended, essentially cylindrical first electrode 2 and a sheath 4 which at least partially surrounds first electrode 2. First electrode 2 is preferably made of glass, or has a sheath made of glass, and is used as the electrode for the measuring device during the determination of the pH in a material to be measured. In the exemplary embodiment, a chamber is formed between first electrode 2 and sheath 4 in which a second electrode 3, preferably designed as a gel, is situated.

[0028] For the measurement, the front region of the measuring device is inserted into the material to be measured, which is usually a foodstuff, as illustrated by example in FIG. 8, liquid from the material to be measured reaching the area between first electrode 2 and second electrode 3 via appropriate measures (not illustrated in greater detail here) such as a diaphragm, for example. First electrode 2 has an insertion tip on a front end to facilitate insertion into the material to be measured.

[0029] A section of the measuring device, not illustrated in greater detail, has processing and display devices which are not explained in more detail here and which therefore are not illustrated. Both electrodes 2, 3 have an electrical connection to the processing device for the determination and display of the measured value.

[0030] According to the embodiment illustrated in FIG. 1, first electrode 2 is pivotably mounted. To this end, a holding fixture 6 is provided in the region of an end 10 of first electrode 2 facing away from the probe tip. Sheath 4 is made of a flexible material which allows first electrode 2 to pivot. A detailed illustration of the holding fixture according to FIG. 1 is shown in FIG. 2.

[0031] Insertion electrodes made of glass are well capable of bearing a load in the axial direction, but break easily under transverse loads, i.e., under loads applied perpendicular to the axial direction. The pivotable mounting, using holding fixture 6 at end 12 and flexible sheath 4, enables first electrode 2 to resist transverse loads resulting from tilting of the measuring device during insertion into the material to be measured or during withdrawal from the material to be measured, for example. The pivotable mounting does not increase the lateral stability of first electrode 2, but, rather, only allows first electrode for the measuring device according to the present invention to pivot under transverse loads.

[0032] Holding fixture 6 has a recess 8 in which the end section of first electrode 2 is accommodated, a base region 16 of recess 8 forming a support for axial end 12 of first electrode 2 in order to support the probe against axial forces F. In the exemplary embodiment, base 16 of recess 8 has an opening 18 for the passage of connection leads, the diameter of opening 18 being smaller than the diameter of probe 2. The connection lead may also be supplied to first electrode 2 in a groove on the side of the recess or in another suitable manner.

[0033] In the exemplary embodiment according to FIG. 2, first electrode 2 is supported against side face 14 of recess 8 by a ring-shaped element 12A which is designed in the form of an O-ring. Ring 12 is preferably made of an elastomer such as silicone, NBR, or the like. Ring 12A supports the first electrode in the region just under the opening in recess 8. An air gap is formed below ring 12A, between first electrode 2 and side face 14, which allows end 10 of probe 2 situated below ring 12A to move sideways under a transverse load on probe 2, as illustrated in FIG. 2b. Probe 2 pivots about an imaginary hinge point 20, which in the illustrated example is a point on the axis of first electrode 2 which maintains its position when first electrode 2 is pivoted. When ring 12A and sheath 4 have good elasticity, the pivoting motion of the probe ends when probe 2 makes contact with two points on side face 14 or on the upper edge of recess 8. The elasticity of ring 12A and of sheath 4 are preferably matched to one another in such a way that, in order to avoid the danger of breakage, first electrode 2 is not able to pivot until it reaches the edge of recess 8, and that the pivoting range of the first electrode is determined solely or at least substantially by the design of sheath 4.

[0034] First electrode 2 is closely surrounded by sheath 4 in at least one location 22 on sheath 4, with the result that sheath 4 guides first electrode 2 and assists with the pivotable mounting of the first electrode. In order for first electrode 2 to make a pivoting motion, sheath 4 is preferably made of a flexible material such as plastic. Ideally, an imaginary hinge point of sheath 4 coincides with imaginary hinge point 20 of first electrode 2. The hinge point of sheath 4 may be determined by the geometry of the sheath. In the embodiment illustrated in FIG. 1, the inner and outer diameter of sheath 4 increases in the region of holding fixture 6 or in the region of imaginary hinge point 20 of first electrode 2. To this end, sheath 4 preferably has a truncated cone-shaped design in this region.

[0035]FIG. 3 shows a further exemplary embodiment of a holding fixture 6 for the pivotable mounting of first electrode 2. Holding fixture 6 has a recess 8 in which an end section of probe 2 is accommodated, base 16 of recess 8 forming a support against axial forces F. A ring-shaped element 12B having a sleeve-like design which surrounds probe 2 in the region of the end section is provided for lateral support, and is introduced between probe 2 and side face 14 of recess 8. Sleeve 12B is formed from a flexible material, preferably an elastomer, which under a transverse load on first electrode 2 is elastically deformed to enable first electrode 2 to pivot, as illustrated in FIG. 3b.

[0036] The elasticity of sheath 4, which is essential for pivoting of first electrode 2, is matched to the transverse load-bearing capacity of first electrode 2. Thus, to ensure easy handling, sheath 4 should not be so elastic that probe 2 yields to the side, even under small transverse loads for which there is no danger that probe 2 may break, thereby making it more difficult to introduce the probe into the material to be measured.

[0037] A further embodiment of a holding fixture 6 is illustrated in FIG. 4. Holding fixture 6 a has a truncated cone-shaped recess 24 whose lower end, which has the smallest diameter, forms a support for probe 2 against axial forces F. In this embodiment, holding fixture 6A does not provide lateral support for probe 2. Due to the conical shape of recess 24, the first electrode becomes “centered” in the initial position after the transverse load is removed. In this embodiment, lateral stability is ensured by sheath 4 which surrounds probe 2 at point 22 according to FIG. 1. Truncated cone-shaped recess 24 allows probe 2 to pivot under a transverse load on the probe. Sheath 4 which holds the first electrode is part of the support for the insertion electrode. To prevent probe 2 from slipping on the base of recess 24, the smallest diameter of recess 24 at the base of recess 24 is preferably equal to or slightly larger than the diameter of first electrode 2. Recess 24 may have geometric shapes other than a truncated cone, in particular a cylinder, as in FIGS. 2 and 3, precautions being taken as appropriate against slippage of the axial end of the probe on the base of the recess. In these cases as well, lateral stability may be ensured by sheath 4, ring-shaped elements being omitted.

[0038]FIG. 5 shows a cross-sectional representation of a measuring device according to the present invention in which the pivotable mounting of the first electrode is provided almost exclusively by sheath 4, the first electrode being introduced at its end opposite the tip into a very flat recess 26, without further holding means, thereby ensuring that this end of the first electrode is positioned in the center of the measuring device.

[0039] First electrode 2 is closely surrounded by the sheath in the region of the tip, an elastomeric gasket 30 preferably being situated between first electrode 2 and sheath 4. Gasket 30 which is in contact with first electrode 2 allows first electrode 2 to be displaced relative to gasket 30 in order to compensate for the length of the sheath when first electrode 2 is pivoted.

[0040]FIG. 6 shows a further holding fixture 6 b as part of a device for pivotably mounting first electrode 2. Holding fixture 6 b has a ball-and-socket joint having first and second joint halves 7 a, 7 b, first joint half 7 a having recess 26 for accommodating the one end of first electrode 2 in which the end of the first electrode is preferably glued using an adhesive 60. FIG. 6a shows the ball-and-socket joint in the rest position, and FIG. 6b shows the ball-and-socket joint in the swiveled position of first electrode 2.

[0041] A further embodiment of a holding fixture 6 c as part of a device for pivotably mounting first electrode 2 is illustrated in FIG. 7. Holding fixture 6 c has a shank containing a receptacle 28 in which the first electrode is secured, preferably by using an adhesive 30. The shank has a region 9 having a smaller diameter about which the shank is able to pivot under transverse loads.

[0042]FIG. 8 shows a sectional representation of the measuring device according to the present invention in a cross-sectional side view during a measurement. The measuring device is inserted with first electrode 2 and a portion of the sheath into a material to be measured 40, being subjected to a transverse load by lateral forces F, due to the fact that the measuring device is inserted into the material to be measured at an angle and then an attempt is made to pull the measuring device out straight, for example, or due to the fact that the tip of first electrode 2 avoids a solid obstruction in material to be measured 40. Flexible sheath 4 follows the pivoting motion of probe 2, it being possible to compensate for the length at point 22 on the sheath at which probe 2 is surrounded due to the fact that the first electrode is supported by sheath 4 so that the first electrode is slightly displaceable.

[0043] Compared to the measuring devices of the related art, the measuring device according to the present invention has only one sheath, so that smaller holes remain in the material to be measured after the measurement has ended.

LIST OF REFERENCE NUMBERS

[0044]2 First electrode

[0045]4 Sheath

[0046]6, 6 a, 6 b, 6 c Holding fixture

[0047]7 a, 7 b Joint halves

[0048]8 Recess

[0049]9 Region of smaller cross section

[0050]10 Axial end of probe

[0051]12A Ring-shaped element

[0052]12B Ring-shaped element

[0053]14 Side face of recess

[0054]16 Base of recess

[0055]18 Opening

[0056]20 Imaginary hinge point

[0057]22 Location on sheath which surrounds the first electrode

[0058]24 Recess

[0059]26 Recess

[0060]28 Recess

[0061] F Forces 

What is claimed is:
 1. A measuring device having an extended first electrode (2) for insertion into a material to be measured (40) and a sheath (4) which at least partially surrounds the first electrode (2), wherein the first electrode (2) is pivotably mounted.
 2. The measuring device as recited in claim 1, wherein the first electrode (2) is pivotably mounted on one end using a holding fixture (6, 6 a, 6 b, 6 c).
 3. The measuring device as recited in claim 1 or 2, wherein the sheath (4) is made of a flexible material, preferably a flexible plastic.
 4. The measuring device as recited in [omission], wherein a chamber is formed between the first electrode (2) and the sheath (4) in which a second electrode (3) for the measuring device is mounted.
 5. The measuring device as recited in one of the preceding claims, wherein a diameter of the sheath (4) increases in the region of the holding fixture (6).
 6. The measuring device as recited in one of the preceding claims, wherein the first electrode (2) and/or a sheath for the first electrode is made of glass.
 7. The measuring device as recited in one of the preceding claims, wherein the holding fixture (6) has an accommodating recess (8) which forms a support for an axial end (10) of the first electrode (2).
 8. The measuring device as recited in claim 7, wherein lateral support is provided by arranging, between the first electrode (2) and a side face (14) of the recess, a ring-shaped element (12A, 12B) which surrounds the first electrode (2).
 9. The measuring device as recited in claim 7, wherein the ring-shaped element (12A) has an essentially circular cross-section.
 10. The measuring device as recited in claim 9, wherein the ring-shaped element (12A) is situated in the region of the opening in the recess (8).
 11. The measuring device as recited in claim 8, wherein the ring-shaped element has a sleeve-like design, and at least partially surrounds the first electrode (2) at one end section introduced into the recess (8).
 12. The measuring device as recited in one of the preceding claims, wherein the ring-shaped element (12A, 12B) is made of a flexible material, preferably an elastomer.
 13. The measuring device as recited in one of the preceding claims, wherein the recess (8) has a truncated cone-shaped design and forms a support for the axial end (10) of the first electrode (2) at its end having the smallest diameter.
 14. The measuring device as recited in one of the preceding claims, wherein the sheath (4) closely surrounds the first electrode (2) at at least one point (22).
 15. The measuring device as recited in one of the preceding claims, wherein the sheath (4) is situated at the point (22) displaceably with respect to the first electrode (2).
 16. The measuring device as recited in one of the preceding claims, wherein the sheath (4) is detachably placed on the first electrode (2).
 17. The measuring device as recited in one of the preceding claims, wherein the holding fixture (6 b) has a joint (7 a, 7 b).
 18. A measuring device having an extended first electrode (2) for inserting into a material to be measured (40) and a sheath (4) which at least partially surrounds the first electrode (2), wherein the sheath (4) is formed from a flexible material.
 19. The use of a measuring device as recited in one of claims 1 through 14 for measuring the pH in foodstuffs. 